Iran's nuclear agency Thursday announced resumption of uranium enrichment at the country's underground Fordow nuclear facility, a site where, under the 2015 nuclear deal with world powers, it had agreed not to carry out any enrichment or enrichment-related research.

The Atomic Energy Organization of Iran said in a statement the enrichment began overnight and was witnessed by an official from the U.N.'s nuclear watchdog agency.

Iran said it plans to enrich up to the level of 4.5% at the site. That is slightly above the level allowed under the Joint Comprehensive Plan of Action, but breaking that barrier was part of Iran's earlier steps away from the agreement as it calls for the other signatories to help it navigate around U.S. sanctions on its important oil exports.

Iran nuclear deal

The JCPOA was meant to address Western accusations that Iran was working to develop nuclear weapons, which Iran denied, saying its nuclear program was for peaceful purposes such as power generation and medicine. Enriching to 4.5% is far below the level needed to make a nuclear weapon.

In addition to carrying out enrichment at Fordow and enriching at higher levels, Iran has also exceeded limits on the amount of enriched material it is allowed to stockpile and it announced the development of more advanced centrifuges that are used in the enrichment process.

The International Atomic Energy Agency's board of governors is meeting Thursday in Vienna to discuss Iran's nuclear work. The agency's inspectors are tasked with monitoring Iran's compliance with the JCPOA.

Iran abiding by the deal

Before U.S. President Donald Trump announced his decision to withdraw from the deal last year, the IAEA said Iran was living up to its part of the agreement. Trump said the deal did not do enough to prevent Iran from developing nuclear weapons and gave the country too much in the way of sanctions relief. The United States has imposed several rounds of new sanctions against Iran.